—What's behind the door?

—________ [ ]

A. Yes,  it is a ball.                      

B. No,  it isn't a ball.

C. There is a ball.                      

D. It's in front of the door.

下图所示为某种免疫过程示意图，据图回答问题：

若用大剂量的x射线杀死b细胞会使机体（）能力下降；

A.体液调节

B.细胞免疫

C.体液免疫

D.非特异性免疫